Magnetic recording media, such as data cartridge tapes, videotapes, audio tapes, other magnetic recording tapes, floppy discs, etc., enjoy wide use and popularity. Such media have evolved to provide increased recording density or capacity per unit volume, reduced average surface roughness and surface-roughness variability, reduced electromagnetic amplitude degradation caused by roughness and other factors, and increased reliability, as measured by, e.g., read- and write-error rates over extended periods of use. Wind characteristics for magnetic tape are also becoming more and more critical with the advent of narrower data tracks and thinner tape constructions. Data-cartridge formats are among the more challenging formats for wind quality, due to the high tape transport speeds and the absence of reel flanges, for example.
Magnetic recording media generally include a magnetic layer coated onto at least one side of a non-magnetic substrate, e.g., a film in the case of magnetic recording tape applications. The magnetic layer includes magnetic pigment dispersed in a polymeric binder. The magnetic layer also optionally includes other components, such as lubricants, abrasives, thermal stabilizers, catalysts, crosslinkers, antioxidants, dispersants, wetting agents, fungicides, bactericides, surfactants, antistatic agents, nonmagnetic pigments, coating aids, and the like.
With certain designs, the magnetic coating (or “front coating”) is formed as a single layer. In an effort to reduce thickness of the magnetic recording layer, a more recent approach is to form the front coating in a dual layer construction, including a support layer (or “lower layer”) on the substrate and a reduced-thickness magnetic layer (or “upper layer”) formed directly on the support or lower layer. With this construction, the lower layer is generally non-magnetic and is comprised of a non-magnetic powder and a binder. Conversely, the upper layer comprises a magnetic metal particle powder or pigment dispersed in a polymeric binder.
A backside coating, or “back coat”, is applied to the other side of the non-magnetic substrate, e.g., to improve the durability, conductivity, and tracking characteristics of the media. The backside coating also optionally includes a polymeric binder and one or more of the components listed above. The backside coating is generally formulated so as to impart both conductivity and runability to the media. Conductivity is accomplished through the use of conductive carbon in the back coat formulation. One method of imparting runability has been to formulate the back coat so as to be substantially rougher than the magnetic coating, thus allowing for stable tape pack formation during winding of the tape.
It is known in the art to calendar the media during its manufacture, e.g., to pass it through a series of opposed rollers before winding it into a roll, to improve surface smoothness. It is also known in the art to heat soak magnetic tape in wound form, after the coating and calendering processes, to “cure” the tape's coatings and increase the glass transition temperatures of the binder matrices. After the curing is complete, the tape is converted for use in cartridges.
Back coats have been formulated to be very smooth, but with a relatively low concentration of a texture particle to facilitate tape handling. However, during the heat soaking process described above, the texture particles tend to emboss into the magnetic side of the tape, which leads to the formation of “pits” in the magnetic coating. This embossing becomes more pronounced on progressing from the outside to the inside of the roll, due to the increased pressures experienced toward the core of the roll. These pits result in substantial nonuniformity in the magnetic surface and hence degrade its recording properties, particularly at the high densities required for advanced recording tapes.